Vacuum Generator on the Ejector Principle

ABSTRACT

A vacuum generator which operates on the ejector principle. A multi-stage ejector has a plurality of nozzles arranged in a row. An air stream, an air from a compressed air connection flows through these nozzles at high speed to an outlet so that a negative pressure is generated in a valve chamber which surrounds the nozzles. A shut off valve closes the air outlet in an air tight fashion. The valve chamber or an evacuation chamber in which the negative pressure is generated has a conduit which is closed by an aeration valve which cooperates with the shut off valve, by which an aeration conduit for aerated the chambers in which the negative pressure is generatable is opened.

The present invention relates to a vacuum generator on the ejector principle, which has a multi-stage ejector with a plurality of nozzles arranged in a row, through which nozzles an air stream, deliverable via a compressed air connection, is carried at high speed to an air outlet, so that a negative pressure can be generated in a communicating chamber surrounding the nozzles.

Such vacuum generators are used in large numbers especially in industrial production facilities. They have the advantage that they can be supplied via the existing compressed air networks. As a rule, they also need no further electrical connections for their control and can therefore be easily integrated into individual gripping devices.

Vacuum generators with single-stage ejectors are known, in which it is usual to close an air outlet, embodied as a sound damper, in order to undo the vacuum as quickly as possible, so that the workpieces that are held by a gripper that is for instance attached can be quickly released. One disadvantage of single-stage ejectors is their high energy consumption, since because of the poor efficiency of generating negative pressure, there is an especially high demand for compressed air to enable securely holding a workpiece. Moreover, in single-stage ejectors, the compressed air must continue to be applied in order to break the vacuum, and therefore a considerable additional air supply is necessary.

From German Patent Disclosure DE 600 23 654 T2, for example, a vacuum generator of the type referred to at the outset is mentioned; in it, the ejector is embodied in multiple stages. Multiple stages means that two, but preferably three or more, nozzles in succession, experience an overflow of compressed air, so that a certain negative pressure level with less consumption of compressed air can be established.

However, in such multi-stage ejectors, it is not sufficient to close the air outlet for aeration in order to release a workpiece, since because of the narrower cross sections, the re-aeration is unsuitable for quickly undoing the retention forces. As a rule, therefore, in the known multi-stage ejectors compressed air is passed via a bypass directly into the valve chamber, so that the release can be accomplished as fast as possible. However, it has been demonstrated that because of the open air outlet on the one hand and the aeration of the valve chamber, which must also be done, a considerable quantity of compressed air is required, so that the advantage of multi-stage ejectors in Willis of efficiency is partly undone again, especially with short cycling times and the attendant frequent blow-off procedures.

The object of the present invention is to create a vacuum generator which, based on multi-stage ejectors, makes a fast undoing of the vacuum possible with low air consumption.

According to the invention, the object is attained in that in the air outlet, a shutoff valve is provided, by means of which the air outlet can be closed in airtight fashion, and the chamber in which the negative pressure can be generated has an aeration aperture that is closed by an aeration valve by means of which, in cooperation with the shutoff valve, an aeration conduit, for aerating the chamber in which the negative pressure can be generated, can be opened.

The aeration of the chamber, in which the negative pressure can be generated, is done either by means of an aeration conduit discharging into the environment and/or a communication of the aeration conduit with a chamber that is under compressed air, such as the conduit which can serve to introduce a compressed air pulse for tripping the shutoff valve. The compressed air generation itself is preferably shut off via a difference connection, in order to reduce the compressed air consumption upon the initiation of a compressed air pulse, since it is unnecessary for breaking the vacuum.

Preferably, the aeration valve is embodied as a differential pressure valve. In the present case, this means that at the negative pressure, the aeration valve remains closed, since ambient pressure acting via a connection is applied to a movable sealing element on the other side. The release is then effected smoothly by the pressure increase in the previously evacuated [noun missing], for instance after the shutoff valve is tripped.

In the simplest case, the aeration device is then such that the aeration valve, embodied as a differential pressure valve, is located between the aeration conduit toward the chamber around the nozzles and a connecting conduit into the environment, and the cross section of the connecting conduit is preferably greater than the cross section of the aeration conduit. It has been demonstrated that as a result of this embodiment of the cross-sectional ratios, secure aeration of the valve chamber can be achieved when a rapid release of the workpiece is desired, and in particular when compressed air, because of the opening of the aeration valve, is able to flow through the aeration conduit into the previously evacuated area.

In a preferred exemplary embodiment, a diameter of the aeration conduit of 2 mm and a diameter of the connecting conduit of 1.5 mm is provided.

An embodiment in which the aeration valve is a movable element, preferably a ball, which is movable freely in a valve chamber between a position that closes the aeration conduit and a position that closes the connecting conduit, is especially preferred; in an intermediate position of the ball, a communication between the connecting conduit and the aeration conduit is uncovered. The advantage of the second seal is that after the connecting conduit is aerated, an unnecessary escape of compressed air through the connecting conduit is avoided by closing the connecting conduit. This, too, helps reduce the compressed air consumption.

As already addressed, in an especially preferred embodiment of the invention, it can additionally be provided that the valve chamber is in communication with a compressed air conduit, through which a compressed air pulse for tripping the shutoff valve can be introduced. In this way, the compressed air pulse used for the shutoff can additionally be used for aerating the valve chamber, so that the reaction time in aerating the valve chamber is reduced further. The closure of the connecting conduit is especially advantageous here, since the compressed air pulse can then be maximally used for the aeration.

The shutoff valve itself is preferably embodied such that it is movable counter to the action of a restoring spring from a position that uncovers the air outlet to a position that seals off the air outlet. As soon as the compressed air pulse for shutting off the vacuum is interrupted, for instance to release a workpiece that is being held, the air outlet is correspondingly opened again, and a negative pressure is generated again in the chamber around the multi-stage ejector.

As is also usual in the prior art, a sound damper can be provided, through which the air can be blown out from the vacuum generator into the environment in order to reduce ambient noise.

One exemplary embodiment of the invention will be discussed below in conjunction with the appended drawings. In the drawings:

FIG. 1 shows a view of a vacuum generator in the dismantled state;

FIG. 2 shows a section through the installed vacuum generator of FIG. 1.

FIG. 1 shows the individual parts of a vacuum generator 10, whose function will be described in further detail hereinafter in conjunction with FIG. 2, which shows the vacuum generator 10 in cross section. The vacuum generator 10 comprises a housing 12, into which various bores have been made. In a first bore 14 (see FIG. 2), a nozzle body 16 is inserted, which on its inside has a plurality of nozzles in a row, by way of which on the ejector principle, a negative pressure can be generated, via communicating apertures 18 in the nozzle body 16, in a valve chamber 20 between the nozzle body 16 and the wall of the bore 14. The compressed air required for this, which is accelerated in the nozzles to a high-speed air stream, is furnished via a compressed air connection 22, which is flanged to the housing 10 in the vicinity of the aperture in the bore 14 via an adapter 24 and a sealing ring 26.

As can readily be seen in FIG. 2, the bore 14 is embodied as slightly conical, viewed from the compressed air connection 22; at this point it should be mentioned that vacuum generators on the ejector principle, which are embodied in multiple stages with a plurality of nozzles in a row, are already known in the prior art.

The compressed air required for generating the vacuum in the valve chamber 14 then flows via an air outlet 28, to which a sound damper is expediently connected, out into the surroundings. The vacuum 14 that occurs in the valve chamber can be utilized, via a transverse bore 30 communicating with it and connected for instance to one or more suction cups that are intended for handling sheet-metal parts.

In the vicinity of the air outlet 28, a shutoff valve 32 is provided, which is located in a valve bore 34 that intersects the air outlet 28; the valve bore 34 is embodied as a blind bore. A valve slide 36 is seated in the valve bore 34, while the aperture 38 (see FIG. 2) necessary for installing the vacuum generator 10 is tightly closed by means of a blind stopper and a sealing ring 42. A restoring spring 46, which keeps the valve slide 36 in the normal situation in a position in which the air outlet 28 is open, is located between the valve slide 36 and the bore bottom 44 of the valve bore 34 and the bore bottom 44. The valve slide 36 is braced on the blind stopper 40 via a spacer piece 48, and an air chamber 50 remains around the spacer piece 48. This air chamber 50 is in communication, via an air conduit 52, with a second compressed air connection 54, by way of which a so-called blow-off pulse can be supplied, the significance of which will be address hereinafter.

An aeration bore 54 is provided in the compressed air conduit 52, and a closure 56 is screwed into this bore. The closure 56 has a connecting bore 58 in its middle, and that bore discharges into the surroundings. The closure stopper 56 is embodied on one end with a valve chamber 62, in which a sealing ball 64 is freely movable. The sealing ball 64 is movable in the valve chamber 62 freely between a first valve seat, in the position shown in FIG. 2, in which it seals off an aeration conduit 66 from the valve chamber 20, and a second valve seat, in which it seals off the connecting conduit 58. The sealing action of the sealing ball 64, which in combination with the two valve seats forms an aeration valve, operates on the differential pressure principle; that is, as long as a higher pressure is operative in the valve chamber 62 than in the valve chamber 20, the latter is closed off by the sealing ball 64. It has furthermore been demonstrated that the diameter of the venting conduit 58, for achieving especially good function of the aeration valve, is preferably greater than the diameter of the aeration conduit 66; in the exemplary embodiment shown, the diameter of the venting conduit 58 is 2 mm, while the aeration conduit 66 is embodied with a diameter of 1.5 mm. It suffices that the ambient pressure, applied via the connecting conduit 58, acts on the ball 64.

For vacuum generation with the aid of the vacuum generator 10, a compressed air of +6 bar (P), for instance, is applied to the first air connection 22. This air flows through the valve body 16 and in so doing, by the known ejector principle, generates a negative pressure in the valve chamber 20; with the aid of this negative pressure the chamber 30 communicating with the valve chamber 20 is also closed, for instance remotely from the vacuum generator 10, by a gripper in contact with a surface of a workpiece. A typical negative pressure of the kind used for instance for handling metal sheets in automobile manufacturing, is on the order of −0.85 bar (V). The multi-stage construction of a vacuum generator, compared with single-stage ejectors, has empirically been shown to save up to 50% of the compressed air needed while the vacuum is being maintained.

If the evacuated chamber 30 is now aerated via the second compressed air connection 54, for instance for releasing a workpiece, a compressed air pulse can be introduced. The compressed air pulse reaches the air chamber 50 through the compressed air conduit 52 and as a result moves the valve slide 36 counter to the restoring force of the restoring spring 46 into a position that closes the air conduit 28. The compressed air supplied at the first compressed air connection 22 can now no longer flow through the nozzle body 16; instead, through the ejector apertures 18, it reaches the valve chamber 20 and the evacuated chamber 30 and aerates them. It should be noted that the compressed air supplied via the compressed air connection 22 is not absolutely necessary for breaking the vacuum and therefore can be preferably shut off or interrupted to avoid an unwanted loss of compressed air, when the compressed air pulse is introduced through the compressed air conduit 52. Since in multi-stage ejectors the cross sections are relatively small, however, the aeration conduit 66 is also employed for additional aeration of the valve chamber 20. Because of the pressure increase in the valve chamber 20, which quickly exceeds the ambient pressure, the sealing ball 64 lifts from its seat that closes the aeration conduit, so that the compressed air supplied along this path via the compressed air conduit 52 can also reach the valve chamber 20 and contribute to evacuating the evacuated chamber 30. Because the sealing ball 64 is seated on the second seat, in which the venting conduit 58 is closed, no unnecessary losses of compressed air, which could overall increase the compressed air consumption of the vacuum generator 10, can occur, either.

By means of the additional aeration valve, the energy consumption of the vacuum generator 10 can be further reduced by approximately 20% in operation, with faster aeration of the evacuated chamber 30, relative to a conventional multi-stage vacuum generator. As soon as the blow-off procedure has been concluded, either the compressed air supply 22 to the vacuum generator 10 can be shut off permanently, or the compressed air pulse supplied at the second compressed air connection 54 is interrupted, so that the valve slide 36 is moved by the restoring spring 46 back into its position shown in FIG. 2, and because of the compressed air now flowing freely through the air outlet 28, a vacuum can quickly build up again in the vacuum chamber 20 and the chamber 30. As a result, the sealing ball 64 is result sucked back against its seat that closes the aeration conduit 66. 

1. A vacuum generator on the ejector principle, which has a multi-stage ejector with a plurality of nozzles arranged in a row, through which nozzles an air stream, deliverable via a compressed air connection, is carried at high speed to an air outlet, so that a negative pressure is generated in a valve chamber surrounding the nozzles, wherein in the air outlet, a shutoff valve is provided, by means of which the air outlet is closable in airtight fashion, and the valve chamber or an evacuation chamber in which the negative pressure is generated has an aeration conduit, which is closed by an aeration valve by means of which, in cooperation with the shutoff valve, an aeration conduit for aerating the said chambers, in which the negative pressure is generatable, is openable.
 2. The vacuum generator of claim 1, wherein the aeration valve is embodied as a differential pressure valve.
 3. The vacuum generator of claim 1, wherein the aeration conduit is connectable to a chamber that is subjected to compressed air.
 4. The vacuum generator of claim 2 wherein the aeration valve is located between the aeration conduit and a venting conduit into the surroundings.
 5. The vacuum generator of claim 4, wherein the cross section of the venting conduit is greater than the cross section of the aeration conduit.
 6. The vacuum generator of claim 5, wherein the venting conduit has a diameter of approximately 2 mm, and the aeration conduit has a diameter of approximately 1.5 mm.
 7. The vacuum generator of claim 1, wherein the aeration valve is a movable element, which is movable freely in a valve chamber between a position that closes the aeration conduit and a position that closes the venting conduit.
 8. The vacuum generator of claim 7, wherein the valve chamber is in communication with an air conduit, through which a compressed air pulse for tripping the shutoff valve can be introduced.
 9. The vacuum generator of claim 1, wherein the shutoff valve is movable, counter to the action of a restoring spring, out of a position that opens the air outlet into a position that seals off the air outlet.
 10. The vacuum generator of claim 1, including a sound damper, via which the air flowing through the air outlet is carried. 